One of the most common defects found in Copper interconnect is buried voids, which is known as a major source of yield loss and reliability degradation.
Detection of Copper voids is an unmet challenge.
Copper film is opaque at visible and UV wavelengths where most of the commercially available optical inspection tools are operating.
In addition—the escape depth of energetic particles such as electron-beam (e-beam) generated signals is limited. High beam energy helps escape in the case of inelastic interaction, but causes concerns over potential damage incurred to low-k film, another essential material for the advanced interconnect technology.
Buried voids close to surface might be detectable by traditional e-beam inspection, which however suffers from high nuisance rate and low capture rate since other contrast mechanisms such as the grainy Copper surface might participate in image formation as well.
There is a growing need to provide systems and methods for efficiently detecting voids in interconnects.